This invention relates generally to sequential timers and, more particularly, to a switch control mechanism which ensures that the power to the control switches in the timer is off as the timer shaft is rotated to select a particular portion of the cycle.
Home laundry appliance timers employ a program cam or cam assembly which is rotated by a motor in one direction to close the proper combination of circuits at predetermined times and to open the same. Such circuits control the washing, extracting, rinsing, drying, and the like of a washing machine. Frequently, the operator desires to alter the prescribed program, and therefore the timer typically includes a manual knob for advancing the main timing cam. Some time after the invention of the automatic clothes washer, it became apparent to both the manufacturer and user of the equipment that damage to various components, including the program timer, could be caused by rapid rotation of the program timer shaft with the power connected to the timer and through it to various machine components. Most instruction books caution the user to turn the appliance off by proper indexing of the timer shaft (either "push to off" or "pull to off"), which disconnects a series switch in the timer, shutting power off to all control switches in the timer and thereby disconnecting power to other components of the machine. If these instructions are not followed, damage usually occurs to the program timer, and as a result of the program timer failure, other components can be damaged. The most common failure in the program timer is contact-welding, which is a result of switching high current through minimal air gaps and opposite voltage polarity during rapid rotation of the shaft.
Devices such as clutch knobs, positive stops, and timer shaft lock-up in the timer-energized position have been developed to protect the machine components and most have been effective. These devices, however, have been expensive or have had other undesirable operational characteristics.
One such fail-safe arrangement is set forth in U.S. Pat. No. 3,033,054 . In that patent, the patentee provides a cam arrangement between a timer shaft and a timer shaft extension having a knob associated therewith so that, upon turning the knob, the timer shaft extension is cammed axially relative to the timer shaft to actuate a switch to open the timer circuit. However, since the timer shaft extension is axially movable relative to the fixed timer shaft, it is possible to override the safety feature by holding the knob outwardly relative to the timer shaft as the main cam is indexed to thus prevent operation of the cam and the opening of the circuit. Furthermore, the arrangement shown in the patent reauires a substantially redesigned timer, since the vast majority of timers have axially movable timer shafts which operate a switch for a "push to off"or "pull to off" safety feature.